The sea and ocean bottoms of the world have experienced a great deal of transformation over the past few decades. For example, large numbers of well heads, pipelines and platforms have been constructed during the offshore exploration of continental shelves for oil and gas in major bodies of water such as the Gulf of Mexico and the North Sea. In addition to such man-made facilities, which also have included undersea communication cables, the sea bottoms have been disturbed by the results of war, accidents and natural occurrences.
In order to generate and maintain records of such construction and other man-made or natural phenomena, sea and ocean surveying has been extensively conducted over the years to develop drawings, maps and other descriptions of surface and underwater boundaries and objects in areas of economic and other importance. For example, waters offshore of many countries have been divided into sectors or blocks which can be used as legal descriptions of their locations in which valuable deposits of oil, gas and other minerals may be found. The location of existing surface and submerged objects, such as platforms and buried pipelines, is also required for various reasons including the safe positioning and construction of new offshore facilities.
However, surveying during the early years of offshore exploration and cable laying was quite difficult and prone to considerable error due to a lack of known fixed points on which to base measurements and because of other factors. Drawings and maps were often made from imprecise knowledge of a vessel's or buoy's position because of inaccurate navigation systems or the action of wind and waves, as well as from faulty surveying equipment or operator error.
Although the recent use of laser surveying equipment and satellite navigation techniques has promoted better accuracy in making new offshore drawings and maps, many older maps still in use are often incorrect in varying degrees. Such older "as built" drawings can have errors of many feet in regard to the actual location of a specific point thereon. Moreover, when navigating a vessel to a specific site, even the most modern satellite navigation systems can be off a number of feet, thus potentially resulting in the vessel being a substantial distance away from the actual location of the map object.
Such flawed maps, imperfect navigational systems, personnel operating errors and adverse sea action, therefore, can create significant expense and waste valuable time when trying to locate a specific map object for repair, modification or removal, especially when the object is underwater and requires a diver to conduct a search therefor. Underwater diving operations for many purposes can be hampered by the lack of visibility due to the turbidity or depth of water in which the diver finds himself, or because a submerged object is also buried below the sea bottom or mud line. This is especially true if the diver is attempting to locate a submerged object which is some distance away from his current position and cannot be seen. With zero or near zero water visibility, a diver also can become confused and disoriented so that he does not know north, south or other directions.
One striking example of the problems encountered under such circumstances is when the diver is attempting to locate, or to verify the map location of, a submerged object buried beneath the sea bottom like a pipeline or a valve component thereof. For example, if a barge is laying a new pipeline near to or over an existing buried pipeline, a diver must first find the exact location of the existing pipeline in order to avoid damage to these facilities. It also may be that a buried pipeline valve needs repair or replacement by a diver who must search for and find this valve. In one prior art procedure for accomplishing this sub-bottom "search and find" mission, the dive support vessel is navigated to a "fix" point at the assumed geographical location of the buried pipeline valve shown on the relevant "as built" map of the offshore area. A bottom-weighted buoy is usually deployed to mark the vessel's "fix" at this map location. The diver, who is typically weighted down, then descends to the sea bed and is provided with a search line of predetermined length which is attached to the buoy weight. He next walks in a circle while holding the line taut, after which another section of line may be added and a larger circle walked. While moving, the diver repeatedly probes the sea bottom with a rod until the buried pipeline valve is discovered.
However, this well known search method is very often performed with the diver in a state of disorientation and loss of direction because of the lack of underwater visibility. If the sea bottom is relatively soft or is overlaid with layers of silt, a diver often finds himself knee-deep in sand or mud while walking which can be physically exhausting. He also is at a great disadvantage if the vessel's navigational "fix" or the "as built" area map has inaccuracies. Many real time diving hours are expended to no avail due to inaccurate information. Moreover, his time on the bottom for deep dives is very limited and he must be regularly brought to the surface in a controlled manner to avoid getting decompression sickness before diving again at some later time.
Another current search technique for locating underwater objects lying on top of a sea bed is to place a sonar transmitter/receiver on the sea bottom so that sonic waves reflected from the diver and such objects are shown as echo images on a shipboard or other remote station monitor. Based on the location of these monitored images which represent the diver and objects to be located, a remote station operator then gives audio commands to the diver via a telephone cable in an effort to guide or direct his movements to these objects. However, such remote audio guidance also has not proven to be particularly efficient either in diver time or effort because of the directional disorientation he experiences due to a lack of visibility. Furthermore, submerged objects which are buried below the mud line or sea bottom will not be detected by sonar beam energy and thus cannot be displayed to the remote operator.
A U.S. Pat. No. 3,045,206 (Ahrens et al) also shows the use of a self-contained sonic transducer/CRT device which is carried by a diver to help him locate underwater objects whose sonar images he views on the CRT screen that may be either outside or inside his helmet. A sonar device with similar functions is also shown in U.S. Pat. No. 3,800,273 (Rolle). However, the Ahrens and Rolle devices do not also permit the diver to view an image of himself in relation to other object images nor will they detect buried or sub-bottom objects. In U.S. Pat. No. 4,102,203 (Sylvester et al), the signals from an underwater ultrasonic testing transducer operated by a diver are transmitted to a remote station for analysis and visual display, from whence visual image test result signals are sent back to the diver for display on his own monitor; however, the Sylvester system is not designed for nor capable of locating the position of underwater objects and directing the diver thereto.
Other guidance methods and means are shown in U.S. Pat. No. 3,541,717 (Grayson) and in an article by Saltzer entitled "A Deep Submergence Divers' Navigation System," Navigation, Vol. 17, No. 1, Spring 1970, pp. 76-82. The Grayson patent is concerned with fish seining operations wherein a search boat sonar unit displays to the search boat operator the position of a body of fish while a purse boat transponder also displays the purse boat's location to the search boat operator, so that the search boat operator can verbally radio a course of travel to the purse boat for directing it to a position where the fish can be caught. The Saltzer article describes a diver's navigation system which visually displays several pieces of information to the diver, e.g., the relative bearing from his location to one or more active pinging acoustic beacons, and his bearing relative to an omnidirectional acoustic broadcasting array. Neither Grayson or Saltzer, however, can assist a diver in locating unmarked objects buried beneath the sea bottom.
Thus, it is very important to create the most efficient conditions possible when conducting underwater "search and find" operations, particularly if the objects searched for are hidden from view under the sea bed. The present invention addresses and overcomes many problems encountered by a diver because it provides map directional information to the diver in finding his way to submerged objects under adverse conditions or in navigating within an underwater area for whatever reasons.